(1) Field of the Invention
The invention relates to a method of fabricating a photoresist mask, and more particularly, to a method of fabricating a bi-layer photoresist mask that will improve critical dimension control in the manufacture of integrated circuits.
(2) Description of the Prior Art
Device sizes continue to shrink as semiconductor manufacturing processes are improved. Continuing advancement in the production of ever smaller devices is limited by photolithography techniques. Dry development processes can increase the overall process window for micro-patterning techniques. Dry development processes can improve resolution and depth of focus and result in more vertical resist profiles. However, the critical dimension bias between isolated and dense lines is too large. That is, because of microloading, isolated lines etch faster than dense lines resulting in an unacceptable difference in critical dimension. Also, after dry development in the bi-layer resist process, the resist line edge is very rough. This will cause imprecision in etching.
U.S. Pat. No. 5,545,512 to Nakato and U.S. Pat. No. 5,286,607 to Brown teach a bi-layer resist process in which a silylated layer is formed between the bi-layers. O2 dry development is used. U.S. Pat. No. 4,882,008 to Garza et al disclose a silylation process and O2 dry development of the resist using NO as the oxygen source.
A principal object of the present invention is to provide an effective and very manufacturable method of providing improved critical dimension control in photolithography.
Another object of the present invention is to provide a method of fabricating a photoresist mask with improved critical dimension control.
A further object of the present invention is to provide a method of fabricating a bi-layer photoresist mask with improved critical dimension control.
A still further object of the invention is to provide a method of fabricating a bi-layer photoresist mask with a reduced critical dimension bias between isolated and dense lines.
Yet another object of the invention is to provide a method of fabricating a bi-layer photoresist mask with a reduced critical dimension bias between isolated and dense lines by using a high SO2 gas dry development process.
Yet another object is to reduce edge roughness of a bi-layer photoresist mask after dry development.
A still further object of the invention is to reduce edge roughness of a bi-layer photoresist mask after dry development by adding an ashing step.
Yet another object of the invention is to provide a method of fabricating a bi-layer photoresist mask with a reduced critical dimension bias between isolated and dense lines and reduced edge roughness.
In accordance with the objects of this invention a new method of forming a bi-layer photoresist mask with a reduced critical dimension bias between isolated and dense lines and reduced edge roughness is achieved. A layer to be etched is provided on a semiconductor substrate wherein the surface of the layer has an uneven topography. The layer to be etched is coated with a first planarized photoresist layer which is baked. The first photoresist layer is coated with a second silicon-containing photoresist layer which is baked. Portions of the second photoresist layer not covered by a mask are exposed to actinic light. The exposed portions of the second photoresist layer are developed away. Then, portions of the first photoresist layer not covered by the second photoresist layer remaining are developed away in a dry development step wherein sufficient SO2 gas is included in the developing recipe to reduce microloading to form a bi-layer photoresist mask comprising the first and second photoresist layers remaining. Thereafter, the bi-layer photoresist mask is ashed to smooth its sidewall edges. This completes formation of a bi-layer photoresist mask having a reduced critical dimension bias between isolated and dense lines and reduced edge roughness.